In the display technology field, the flat panel device possesses advantages of high image quality, power saving and thin body. Thus, it has been widely applied in various consumer electrical products, such as mobile phone, television, personal digital assistant, digital camera, notebook, laptop, and becomes the major display device.
The common flat panel display device at present mainly comprises a Liquid Crystal Display (LCD) and an Active Matrix Organic Light-Emitting Diode (AMOLED). The Thin Film transistor (TFT) is a main drive element in the LCD and the AMOLED display devices. A plurality of thin film transistors are aligned in array on the TFT substrate.
Generally, in the active matrix display device, and particularly in the OLED, the importance of the threshold voltage (Vth) is significant. The stable, uniform threshold voltage can make the display brightness of the OLED be more even and the display quality be higher. The dual gate thin film transistor (Dual-gate TFT) possesses better performance than the common single gate thin film transistor (single-gate TFT). For example, the electron mobility is higher, and the current of activation state is larger, and the subthreshold swing is smaller, and the stability and the uniformity of the threshold voltage are better, and the gate voltage bias and the light stability are better.
In the manufacture process of the OLED, for reducing the difficulty of the manufacture and preventing the deterioration and unevenness of the chromaticity and brightness of the organic light emitting material, the display method of white organic light emitting diode in cooperation with the Color Filter (CF) is commonly utilized. The manufactured of the color filter in the white light OLED display device is mainly to perform coating after accomplishing the array manufacture process of the TFT substrate. Namely, the Color Filter On Array (COA) technology is utilized.
As shown in FIG. 1, a dual gate TFT substrate structure utilizing COA skill according to prior art comprises:                a substrate 100;        a bottom gate 200, a bottom gate isolation layer 300, an active layer 400, an etching stopper layer 500, a source/a drain 600 stacking up on the substrate 100 from bottom to top in orders;        a passivation layer 700 positioned on the source/the drain 600 and the etching stopper layer 500;        and a top gate 810 and a color filter 830 positioned on the passivation layer 700.        
In the dual gate TFT substrate structure utilizing COA skill, the top gate 810 and the color filter 830 are positioned at the same layer, which are on the passivation layer 700. The color filter 830 merely functions for filtering the light. The passivation layer 700 is employed to be the top gate isolation layer of the top gate 810 at the same time. Thus, the passivation layer 700 requires great stability and tightness. In prior art, the inorganic material possessing great tightness and stability, such as Silicon Oxide or Silicon Nitride is utilized. In relatively higher temperature environment, which is generally above the 350° C., the passivation layer 700 is deposed and formed. The technical problem of this is: the gas of deposing the passivation layer 700 at high temperature will enter the thin film deposed in the previous manufacture process and change the property of the isolation layer or the active layer, or cause the metal electrode hillock phenomenon. Ultimately, the abnormality of the TFT electrical property can caused thereby.